Nitrogen oxyanion reduction by Co(ii) augmented by a proton responsive ligand: recruiting multiple metals

Abstract

Deoxygenation of nitrite oxygen with divalent cobalt was achieved using (PNNH)CoCl₂, carrying a pyridyl pincer ligand with one P(t-Bu)₂ arm and one pyrazole arm. Reaction of (PNNH)CoCl₂ with NaNO₂ at a 2 : 5 mole ratio promptly forms equimolar (PNNH)Co(NO₂)₃ and (PNN)Co(NO₂)(NO), {CoNO}8 with the lost ligand proton combined with removed oxo as hydroxide. These two Co^III products are characterized, showing a bent CoNO unit as the fate of the reduced nitrogen. DFT calculations are consistent with two one-electron Co^II reductants binding to one NO₂⁻ bridge, then proton transfer being needed for facile N/O bond scission. A species detected by low temperature execution of this reaction contains cobalt in two oxidation states with an N,O bridging nitro group and pincer ligands that have been deprotonated, showing the active participation of the proton responsive ligand.